This invention generally relates to air recovery electrochemical cells.
Batteries are commonly used electrical energy sources. A battery contains a negative electrode, typically called an anode, and a positive electrode, typically called a cathode. The anode contains an active material that can be oxidized; the cathode contains an active material that can be reduced. The anode active material is capable of reducing the cathode active material. In order to prevent direct reaction of the anode material and the cathode material, the anode and the cathode are electrically isolated from each other by a separator.
When the battery is used as an electrical energy source in a device, electrical contact is made to the anode and the cathode, allowing electrons to flow through the device and permitting the respective oxidation and reduction reactions to occur to provide electrical power. An electrolyte in contact with the anode and the cathode contains ions that flow through the separator between the electrodes to maintain charge balance throughout the battery during discharge.
An air recovery battery, also known as an air assisted or air restored battery, is a battery that uses air to recharge its cathode during periods of low or no discharge. One type of air recovery battery employs zinc powder as the anode, manganese dioxide (MnO.sub.2) as the cathode, and an aqueous solution of potassium hydroxide as the electrolyte. At the anode, zinc is oxidized to zincate: EQU Zn+4OH.sup.-.fwdarw.Zn(OH).sub.4.sup.2- +2e.sup.-
At the cathode, MnO.sub.2 is reduced to manganese oxyhydrate: EQU MnO.sub.2 +H.sub.2 O+e.sup.-.fwdarw.MnOOH+OH.sup.-
When the cell is not in use or when the rate of discharge is sufficiently slow, atmospheric oxygen enters the cell and reacts with the cathode. Manganese oxyhydrate is oxidized to form MnO.sub.2 : EQU 1/2O.sub.2 +MnOOH.fwdarw.MnO.sub.2 +OH.sup.-
During high rates of discharge, air recovery batteries operate like conventional alkaline cell by reducing "fresh" (unreduced) MnO.sub.2. During low rates of discharge and periods of rest with no current flow, the "consumed" (reduced) MnO.sub.2 is restored or recharged by atmospheric oxygen to the fresh state. Since oxygen must reach the MnO.sub.2 for recharging, the cathode of the battery must not be wetted completely by electrolyte. If the cathode is soaked with wet electrolyte, air transport properties inside the cathode degrade and recharging of MnO.sub.2 is hampered.
A prismatic battery can be generally rectangularly shaped. For example, a prismatic battery can be relatively flat with two parallel rectangularly-shaped faces, making them suitable for use in cellular telephones. More broadly, a prismatic battery can be shaped as a polyhedron with two polygonal faces lying in parallel planes and with the other faces as parallelograms. For example, if the polygonal faces are rectangular, then the battery is shaped as a rectangular prism. If the polygonal faces are circular, then the battery is shaped as a circular prism.